1. Field of the Invention
The present invention relates to an ink jet printer for forming desired characters or images by emission of liquid ink in the form of droplets, and more particularly to such ink jet printer capable of realizing constant ink droplet emission regardless of the temperature dependence of ink viscosity.
2. Description of the Prior Art
There are already known and used various types of ink jet printer. Such ink jet printer is generally provided with an electrostriction element which is associated with a part of an ink chamber storing the ink and is deformed by the application of a determined voltage to reduce the volume of said ink chamber, thereby emitting an ink droplet with a diameter in a range of 50-100 .mu.m from an ink nozzle of a corresponding diameter provided in said ink chamber. The ink suitable for used in such ink jet printer has to have certain physical properties for dot formation mechanism, and is provided generally with a viscosity in a range of 2-10 cp and a surface tension in a range of 40-50 dyne/cm.sup.2. Among these properties, the viscosity has a particularly strong temperature dependence and may easily be located out of the appropriate range even in a temperature range of 0.degree.-40.degree. C. in which the apparatus has to show normal function. Particularly at a low temperature the normal ink emission is often hindered by a high viscosity.
In order to avoid such drawback there has been employed a heating device for maintaining the ink at an appropriate temperature. However, though such method is effective for achieving appropriate physical properties when the ink is maintained at a constant temperature, such method inevitably requires a certain time for heating the ink to a determined temperature after the power supply is turned on, thus causing a delay before the printer becomes functionable.